options: Remove parsing `--verbose` from the configuration file

The --verbose option is only used by flake8, itself, when parsing
and handling preliminary options. After parsing and merging options
from the configuration file, there is no other behavioral impact to the
core of flake8. In other words, setting verbose = ... in a
configuration file doesn't change the logging verbosity.

While the FileProcessor does expose a verbose attribute, obtained
from the parsed options, the verbosity of the core of flake8 should be
consistent with how a plugin may respond to the attribute's value.